This invention relates to charging flowable materials into selected cells of a honeycomb structure and, more particularly, to a method and apparatus for selectively manifolding (i.e., plugging) cells of a honeycomb structure for the fabrication of filter bodies and other selectively sealed honeycomb structures.
Honeycomb structures having transverse cross-sectional cellular densities of approximately one-tenth to one hundred cells or more per square centimeter, especially when formed from ceramic materials, have several uses, including solid particulate filter bodies and stationary heat exchangers, which require selected cells of the structure to be sealed by manifolding or other means at one or both of their ends. The term "sealed" and its other corresponding grammatical forms (i.e. sealant, sealing, etc.) are used herein to refer to both porous and non porous means of closing the open transverse cross-sectional areas of cells.
It is well known that a solid particulate filter body may be fabricated utilizing a honeycomb structure formed by a matrix of intersecting, thin, porous walls which extend across and between two of its opposing end faces and form a large number of adjoining hollow passages or cells which also extend between and are open at the end faces of the structure. To form a filter, one end of each of the cells is sealed, a first subset of cells being sealed at one end face and the remaining cells being sealed at the remaining opposing end face of the structure. Either of the end faces may be used as the inlet face of the resulting filter. The contaminated fluid is brought under pressure to an inlet face and enters the body via those cells which have an open end at the inlet face (i.e., "inlet" cells). Because these cells are sealed at the opposite end face ("outlet" face) of the body, the contaminated fluid is forced through the thin, porous walls into adjoining cells which are sealed at the inlet face and open at the outlet face (i.e., "outlet" cells). The solid particulate contaminant in the fluid which is too large to pass through the porous openings in the walls is left behind and a cleansed fluid exits the filter body through the outlet cells for use.
Rodney Frost and Irwin Latchman describe in a copending application Ser. No. 165,646, filed July 3, 1980, entitled FILTER AND RELATED APPARATUS, now abandoned and assigned to the assignee of this application, a most efficient solid particulate filter body formed from a honeycomb structure in which the cells are provided in transverse, cross-sectional densities between approximately one and one hundred cells per square centimeter with transverse, cross-sectional geometries having no internal angles less than thirty degrees, such as squares, rectangles, equilateral and certain other triangles, circles, elipses, etc. The cells are also arranged in mutually parallel rows and/or columns. Alternate cells at one end face are filled in a checkered or checkerboard pattern and the remaining alternate cells are sealed at the remaining end face of the structure in a reversed pattern. Thus formed, either end face of the filter body may be used as its inlet or outlet face and each inlet cell shares common thin, porous walls with only adjoining outlet cells, and vice versa. Other cellular cross-sectional geometries and other patterns of sealed cells may be employed to fabricate effective, although perhaps less efficient filter bodies than those of Frost and Lachman.
For the mass production of such filters, it is highly desirable to be able to seal selected cell ends as rapidly and as inexpensively as possible. Frost and Lachman in the previously referred to application Ser. No. 165,646 describe fabricating filter bodies by manifolding (i.e., plugging) the end of each cell individually with a hand-held, single nozzle, air actuated gun. The hand plugging of individual cells by this process is long and tedious and is not suited for the commercial production of such filters and other honeycomb structures which may have thousands of cells to be selectively sealed. Frost and Lachman also postulate the use of an array of nozzles so that the sealing material may be simultaneously injected into a plurality or all of the alternate cells at each end face of the honeycomb structure. However, a working model of this device is not known to exist for plugging honeycomb structures having these higher cell densities.
In a copending application Ser. No. 283,733, filed July 15, 1981, entitled IMPROVED METHOD AND APPARATUS FOR SELECTIVELY CHARGING HONEYCOMB STRUCTURES and assigned to the assignee of this application, Rodney Frost and Robert Paisley first describe the use of a mask having a number of openings extending through it for selectively manifolding honeycomb structures in the fabrication of solid particulate filter bodies. Their embodiment was a rigid plate having a number of bores.
Masks have also been formed for manifolding cells which are regularly interspersed among substantially mutually parallel rows and substantially mutually parallel columns at an open surface of a honeycomb structure by applying strips of an adhesive backed flexible webbing impermeable to the sealing material, such as masking tape, over selected rows and columns of cells or, alternatively, by providing a matrix of spaced, overlayed strips of a resilient, impermeable and reusable material such as metal foil which are joined together and fitted, with or without an underlying gasket, over the open surface of the structure with the openings through the matrix and gasket, if provided, positioned opposite the cells to be charged. By providing a honeycomb structure with cells arranged in mutually parallel rows and mutually parallel columns and covering alternate rows and alternate columns of cells with strips of a suitable flexible material such as the masking tape or the joined thin metal strips, the open ends of one-half of a subset of cells arranged in a checkered pattern across the end face were exposed. After filling the ends of these cells, the strips were removed and strips applied covering the remaining alternate rows and remaining alternate columns thereby exposing the open ends of the remaining half of the subset of cells of the checkered pattern at the end face for filling. Both embodiments provide greater flexibility in dealing with surface height variations and better masking of the cell ends not to be charged including those which may be damaged than does the rigid plate embodiment. However, both embodiments must be applied twice to each end face to manifold all alternate cells at the end face in the desired checkered pattern of Frost and Lachman. This is a significant limitation with respect to the tape strips which must be individually applied across each end face, a time consuming task. The reusable matrix and gasket of the second embodiment may be more quickly applied and removed, but like the rigid plate embodiments, is less easily adapted to distortions in the cell locations at the end faces.
In another embodiment, a rigid plate was provided with a plurality of bores extending therethrough to register with the open ends of alternate cells of a honeycomb structure. Each bore was fitted with a short filling tube which protruded from the face of the plate and into a cell when the plate is aligned over the open cell ends of a honeycomb structure. A sealing material was forced from the opposing face of the plate through the bores into the cell ends receiving the tubes. To some extent, the filling tubes of the first embodiment assisted in aligning the metal plate with the cells to be filled and reduce the likelihood of sealing material being fed into the remaining cell ends covered by the plate. Theis embodiment was essentially inflexible, a limitation which became more significant when cell densities in the honeycomb structure were increased and distortions in the locations of cell walls become relatively more severe. Its rigid construction also sometimes damaged brittle honeycomb structures.
In another embodiment, rigid rivets were attached at regular intervals along lengths of thin flexible strips and run along alternate diagonals of cells arranged in mutually parallel rows and mutually parallel columns, each rivet being inserted into and covering the open end of a cell along the diagonal. In this way, half of the cells exposed at an end face of the honeycomb structure were covered in a checkered or a checkerboard pattern and the open ends of all of the remaining cells filled in a single sequence of steps. The strip-backed rivets were more flexible but required more handling than either of the plate embodiments, lessening their appeal for use in selectively charging honeycomb structures on a commercial basis.
In copending application Ser. No. 283,732, filed July 15, 1981 and entitled IMPROVED METHOD AND RELATED APPARATUS FOR SELECTIVELY MANIFOLDING HONEYCOMB STRUCTURES, now Pat. No. 4,557,773 Roy Bonzo describes manifolding the cells of a honeycomb structure by blocking off the open end faces of the structure with a solid covering applied thereto, preferably a preformed, transparent polymer film, and preferably an adhesive backed polyester film, and forming openings through the covering opposite selected cells at each end face with a suitable tool. In the case of the polyester film, one or more heated probes which melt openings through the film can form the openings. Again due to cellular distortions, the number of probe elements which can be used simultaneously on an opening-forming tool and thus, the number of openings which can be formed by each application of the tool is limited. These indicated shortcomings of the existing art as well as other problems are overcome to various degrees by the subject invention.